1. Field of the Invention
The present invention relates to a signal processing apparatus, a filter apparatus, a signal processing method and a filtering method.
2. Description of the Related Art
In recent years, the speed of operation of transistors has increased as CMOS processes have made miniaturization possible, while the power supply voltage that can be supplied to operate transistors has decreased. Though such decrease in the power supply voltage in some cases places limits in terms of the design of the circuit, it is difficult to place limits on charge domain filter circuits in terms of the design of the circuit caused by decrease in the power supply voltage, and therefore, it is expected that the importance in charge domain filter circuits will further increase in the future.
When a filter circuit, a gain variable amplifier or the like is formed in a wireless communication apparatus using an analog circuit of a continuous time system CMOS circuit in related art, for example, generally an issue arises, such that the dynamic range properties are not good or the properties become inconsistent. In contrast, the charge domain filter circuit described in 2006 IEEE International Solid-State Circuits Conference 26.6 “An 800 MHz to 5 GHz Software-Defined Radio Receiver in 90 nm CMOS” can be easily applied to a filter circuit, a gain variable amplifier or the like provided in a wireless communication apparatus, and a filter circuit or a gain variable amplifier having excellent properties can be implemented.
Concretely, the charge domain filter circuit described in 2006 IEEE International Solid-State Circuits Conference 26.6 “An 800 MHz to 5 GHz Software-Defined Radio Receiver in 90 nm CMOS” is provided with a number of capacitors and a number of switches for electrically connecting each capacitor to an input terminal on the basis of a control signal so that different capacitors sample input signals in sequence. Here, CMOS capacitors, for example, can be used as the capacitors.